Conversion constants are not shown and errors in conversion.

[KaeroDot]

The conversion constants are not shown anywhere in the GUI. Also, the source of conversion constants should be exactly cited so users know how relevant the conversion constants are.

Because:
I have found that Convertidor calculates energy 1.602176634e-19 J = 0.99999958431566282198688 eV, that
is not in todays SI units. SI units states that elementary charge value is exactly 1.602 176 634 x 10-19 C with zero uncertainty (it is defining constant). Maybe you have used some obsolete value of elementary charge before SI redefinition in 2019?
Unfortunately this cause relative error of 4e-7 J/J, that is quite large and measurable error.
Also, Convertidor calculates 1 Wh = 3600.000000000076904510400000431623796058. Again this seems to me as utterly nonsense, but the value and source of conversion coefficient is unknown. However the error here is only in order 1E-14, that is unmeasurable. Yet why the software allows calculation to so many significant numbers eludes me absolutely.

I have used Convertidor version 1.3.0 from flathub.

References:
SI brochure: https://www.bipm.org/en/publications/si-brochure
CODATA values: https://physics.nist.gov/cgi-bin/cuu/Value?e

[GS90]

Thank you for the detailed description of the issue.
Indeed, my energy unit conversions were not entirely accurate.
I have implemented improvements in the new version, 1.3.1.

[GS90]

Regarding showing the conversion constants and their sources: you're right, this is a good idea. But it's a separate task - we need to figure out how to properly add this to the UI. I'll look into implementing this in a future release.

[KaeroDot]

Also, there is another issue. For example, which BTU is implemented? The Wikipedia lists 5 different BTU units, of which at least 2 seems to be daily used. This could be sorted out if conversion factor is shown, however it would be impractical to guess BTU implementation based on the conversion factor. Better is to show which BTU is used directly in some unit description.
Also different foot units are still used in USA. I am sorry for this non-SI mess, unfortunately you allow very high precision and this brings up many many issues in conversions, and more to say about the historical units. For some historical units conversion factors are known only with some uncertainty. E.g. old Egyptian cubit is known only by measuring the real artifact, and this brings out uncertainty of measurement, thus any conversion to cubit is with non-zero uncertainty and arbitrarily high precision has no sense...

Yes, you are right, these are separate tasks and separate issues should be started. I keep my fingers crossed for you and I hope you will manage it, the murky waters of non-SI world is hard to navigate! :)

https://en.wikipedia.org/wiki/British_thermal_unit
https://www.nytimes.com/2020/08/18/science/foot-surveying-metrology-dennis.html